This invention relates generally to fluid-jet writing systems and more particularly to those systems which utilize a mechanical pump for pumping writing fluid from a fluid container or reservoir to one or more printing or writing fluid-jet nozzles. Although a variety of writing fluids may be used in such systems, the term "ink" shall be used hereinafter for convenience in referring to all such writing fluids.
In general, writing devices of the type described have heretofore been constructed and arranged so that fluid pressure is developed within the system only when the fluid jet nozzles are actuated to produce printed material. Thus, during periods of inactivity, the fluid pressure is permitted to drop and only upon actuation of the system is the fluid pressure increased to operational levels. This is usually accomplished by means of a constant speed pump which can develop a fluid pressure and flow rate which do not necessarily correspond to the ink pressure and flow rate required at the nozzles. In order to control the fluid pressure a spring-loaded pressure control valve is generally employed on the downstream side of the pump.
The previously known systems described above have several deficiencies, one of which involves the reduction in ink pressure during periods of inactivity. As a consequence, once the system is actuated a time lag occurs between the moment of actuation and the moment that ink actually issues from the nozzles, at the appropriate pressure, to produce a clear recordation of the printed characters.
Furthermore, since air bubbles often enter the system during periods of inactivity, an ink splashing effect may intermittently occur at the nozzles for a period of time, thereby again causing unclear and unsatisfactory printing.
In addition, the spring-loaded pressure control valve cannot normally maintain the ink pressure at a predetermined value except within rather broad ranges. Thus the quality of the printing is also adversely affected by rather substantial variations in the pressure of the ink at the nozzles.
Objects of the present invention are to provide a fluid-jet writing system of the type generally described above, but which is improved in a manner whereby ink pressure is maintained even during periods of inactivity, and the pressure is always maintained with a high degree of exactness, whereby to effect a higher quality of writing and to avoid delays in printing upon actuation of the system.